Tubular stock is used as a basic raw material in the manufacture of innumerable products including automotive exhaust systems, automotive structural and drive line components, furniture, bicycles, fencing, and conduit for electrical lines, fluids and gases. Metal tubes are commonly produced by a cold-forming process wherein flat stock is removed from skegs, progressively roll-formed to a near tubular shape and closed to form the tube by heating the opposite exposed edges of the partially formed stock and forging them together. Alternatively, tubular stock can be formed by a hot extrusion process.
Once formed, the tubular stock must be cut into manageable lengths. Typically, this takes place on-line with the production of the tubing through the use of an apparatus which is capable of moving in synchronism with the tubing and cutting it on the fly. Such devices include saws and guillotines using hardened steel blades.
The lengths of tubes which are cut in the primary process described above are typically fairly long; i.e., 20 feet or more in length. These lengths are often subsequently re-cut into shorter lengths for final fabrication. Re-cut devices fall into two categories: (1) saws and guillotines which drive a blade through the stock and (2) supported shears in which part of the tooling is internal of the workpiece during the shear operation. Within the tube shearing technology, the automatic feed apparatus described herein and the methods of operating same apply exclusively to supported shears; however, the feed apparatus and methods may be applicable to any workpiece treatment mechanism involving passage of the workpiece over a mandrel; e.g., a tube bender. In addition, certain of the components described herein are suitable for numerous applications outside of the supported shear technology.
Supported shear devices typically involve first and second dies which are disposed immediately adjacent one another along the longitudinal path which the tubular workpiece follows as it passes through the shear dies and which are movable under power relative to one another along an interface which defines the shear plane. Proper shearing action requires that the workpiece be supported internally by a mandrel in the area of the shear plane. A short but valuable description of the supported shear process may be found in the Tube and Pipe Quarterly, Volume 7, No. 2, March/April 1996, "The Basics of Supported Shear Cutting," pages 28-30.
A substantial advance in supported shear devices was made by Alexander Borzym in the 1980's and is recorded in U.S. Pat. No. 4,635,514 issued Jan. 13, 1987. In that device one of the two adjacent dies is caused to reversibly move relative to the other through an orbital or elliptical path by a specially designed drive system. Mr. Borzym's invention was an improvement over the prior art devices in which the relative die movement is in an L-shaped path.
While the supported shear is typically used as a re-cut device, it is advantageous to provide the capability for automatically feeding the master lengths of tubing into the shear device. This function is complicated by the presence of a feed stop and by the mandrel and the support rod by which the mandrel is held in place within the shear plane.
Prior art devices have supported the mandrel within the shear plane on a rod which extends away from the shear device in the exit direction such that the cut lengths of tubing accumulate on the mandrel rod. These cut lengths must periodically be removed by reverse feed or by periodically withdrawing the mandrel rod. See also U.S. Pat. No. 4,631,998 in which both the mandrel and the rod are periodically withdrawn to remove cut tube lengths.